For most aspects of energy conservation, the bigger the tree the better. Larger trees shade larger areas. Though not an energy-saving feature, large trees also store more carbon. In some ways, trees that use more water save more energy too, since they transpire more water, leading to more evaporative cooling of the surrounding environment.
On the other hand, if trees need to be artificially watered, although they provide evaporative cooling, that energy conservation benefit is offset by the energy expenditure to provide water. By choosing drought-tolerant trees in dry sites or environments, you can still provide cooling shade without tapping into other energy resources.